Measurement of the emg-force relationship during voluntary and exercise-induced contractions in a human upper airway muscle. Fuller, David, Jennifer Sullivan, Elik Essif, Kirkwood Personius, and Ralph F. Fregosi. Department of Exercise & Sport Sciences and Department of Physiology, The University of Arizona Health Sciences Center, Tucson, AZ 85721.
APStracts 2:0126A, 1995.
The upper airway muscles play an important role in breathing, swallowing, and speaking, but little is known about the EMG-force relationship of these muscles. We have measured the peak integrated EMG activity (iEMG) and force of human nasal dilator muscles (NDM) with a custom-designed head piece that was attached via the forehead and upper lip. The head piece contains a micromanipulator that holds a rod with a load-cell mounted on its tip. The reproducibility of the force measurements was examined by measuring the lateral or "flaring" force of the NDM in multiple trials on two separate occasions in 13 subjects. For these studies the subjects were instructed to perform maximal voluntary contractions (MVCs). Test -retest reproducibility averaged 8.3 % (coefficient of variation) for within-day comparisons, and 13.7 % between days. We also measured iEMG and NDM force during an incremental exercise test in 9 of the subjects; they were instructed to breathe nasally throughout one 30 sec epoch at rest and at each work-load. The iEMG and force during peak exercise (175-275 W) averaged 81 +/- 26 (SD) % MVC and 235 +/- 127 mN (about 75 % MVC), respectively. The iEMG during incremental exercise was linearly related to the peak force (r = 0.90, P < 0.001). Contractile properties were measured in 7 of the subjects by applying single, supra-maximal shocks (0.1 ms pulse) to the facial nerve. Twitch force averaged 9 +/- 6 % MVC, and the time to peak force 62 +/- 13 ms, which is considerably faster than human diaphragm or elbow flexors. In conclusion: 1) our method is useful for making reproducible measurements of NDM force during voluntary, involuntary and electrically-evoked contractions; 2) the force measured with this system closely parallels the neural drive (iEMG) to the NDM; 3) the force output of the NDM during peak exercise with nasal breathing (i.e., 75 % MVC) is substantial; 4) human NDM have relatively rapid contractile properties. 

Received 21 July 1994; accepted in final form 14 March 1995.
APS Manuscript Number A745-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on  4 April 1995.